Chlorophyll organization in dark‐grown and light‐grown pine ( Pinus brutia ) and barley ( Hordeum vulgare )

A study was conducted comparing the organization of chlorophyll during development of the photosynthetic apparatus in dark‐grown and light‐grown pine and barley. The rationale was that gymnosperms, but not angiosperms, have a capacity to synthesize chlorophyll in darkness. Seedlings of Pinus brutia were germinated and grown in darkness or under photoperiodic (day/night) conditions. The low‐temperature (77 K) fluorescence spectra of newly‐emerging dark‐grown seedlings exhibited a single fluorescence band peaking at 678–679 nm, which decayed primarily with a ∼5.5 ns lifetime. Over the first few days of growth, the emission shifted to longer wavelengths and a subnanosecond lifetime component became prevalent. After several days of dark growth the emission spectrum and lifetime profile of the low temperature fluorescence came to resemble those of light‐grown pine and barley. At room temperature, dark‐grown pine showed little variable fluorescence, though addition of DCMU caused a substantial fluorescence rise. Illumination with moderate light for a few hours was sufficient to ‘photoinduce’ the appearance of normal variable fluorescence. At 77 K, DCMU‐treated samples clearly showed a very long‐lived (∼40 ns) fluorescence lifetime component in light‐grown pine and barley. This component was undetectable in dark‐grown pine. If, however, dark‐grown samples were illuminated either before or after DCMU addition and then frozen to 77 K, the ∼40 ns lifetime component appeared at a fluorescence intensity similar to that in light‐grown samples. These results are explained primarily in terms of photoactivation of the photosystem II (PSII) donor side. The temporary maintenance of PSII in an inactive, highly‐quenched state is suggested to provide an available, yet protected precursor for active PSII.